Re: Jetty Session ID Prediction

[Amit Klein <aksecurity@xxxxxxxxx>]

Michal Zalewski wrote:
> On Mon, 5 Feb 2007, NGSSoftware Insight Security Research wrote:
>
>   
> > Jetty generates a 64-bit session id by generating two 32-bit numbers in
> > this way, so we end up with an encoded 64-bit integer. By decoding the
> > integer and splitting it into its two component 32-bit integers, we can
> > easily brute-force the generator's internal state.
> >     
>
> Why on earth would you want to brute-force it?
>
> http://www.springerlink.com/content/9jkp3179mj6fwh6m/s
> http://dsns.csie.nctu.edu.tw/research/crypto/HTML/PDF/C89/138.PDF
>
>   

I don't think that the method described in the paper you referenced 
above is applicable as-is, because the method requires that the state of 
the PRNG is known (the coefficients aren't), while in our situation, the 
coefficients are known, but the state isn't known in fullness (only 32 
bits out of the 48 are known).

-Amit